where \(m_{F}\)  is the vector-like mass and \(\lambda _{F}\)  is the Yukawa coupling between
the new Higgs and the vector-like fermions. Since the new fermions live in a non-trivial representation of QCD, one can have
the single production of \(S\)  through gluon fusion, and the decay of into two photons is possible because the new fermions carry electric charge.
This toy model has been studied by several groups, see Refs. [1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]}, [12]}, [13]}, [14]}, [15]}, [16]}, [17]}, [18]}, [19]}, [20]}, [21]}, [22]}.
